Merge pull request #2127 from deepseek-harness/fix/subagent-empty-terminal-message-output

fix(subagent): keep output past an empty terminal message with one selection rule

packages/scaffold/client/tests/fake-runtime.ts

@@ -26,6 +26,8 @@
  *   array; `FAKE_MESSAGE_WITHOUT_DATA`: assistant/message with no data
  *   member; `FAKE_MALFORMED_REASON`: `session.finished` reason is a bare
  *   string (wire-validation probes).
+ * - `FAKE_EMPTY_MESSAGE`: the turn streams a text chunk, then records an empty
+ *   assistant/message for a usage-only max-tokens step.
  * - `FAKE_HANG_INIT`: never answer `initialize` (mid-handshake cancel probe).
  * - `FAKE_INIT_READY` + `FAKE_INIT_GO`: touch the READY file when `initialize`
  *   arrives, then poll for the GO file before answering (deterministic
@@ -117,7 +119,9 @@ function runTurn(sessionId: string): void {
     message: {
       id: `fake-assistant-${seq}`,
       role: 'assistant',
-      content: [{ type: 'text', text }],
+      // Model the usage-only message recorded after a max-tokens step that
+      // assembled no output blocks.
+      content: env.FAKE_EMPTY_MESSAGE !== undefined ? [] : [{ type: 'text', text }],
       source: { kind: 'model', provider: 'fake', model: 'fake' },
     },
   })